A light emitting diode (LED) is a luminous conductive chip having a P-N junction structure, and the main raw material for forming the LED is gallium nitride (GaN). GaN is widely used in the research and industry of semiconductor and solid state lighting, because of its advantages of high efficiency, long life span, and environment friendliness. Group III-V nitrides, for example, GaN, InGaN, AlGaN, and AlGaInN, have an adjustable direct bandwidth of 0.7 eV to 6.2 eV, which covers the spectral range from the bandwidth of ultraviolet (UV) light to that of infrared light. Thus, such nitrides are considered as the most suitable materials for fabricating devices emitting blue light, green light or white light.
Presently, a GaN-based LED generally comprises a GaN layer heteroepitaxially grown on a flat substrate thereof. The substrate includes a sapphire substrate, a silicon carbide substrate, and a silicon substrate. Due to large lattice constant mismatch and large thermal expansion coefficient difference between the substrate and the GaN epitaxial layer, a large number of stress defects and crystal defects may be generated in the GaN epitaxial layer. These defects may form some nonradiative recombination centers, and may decrease the performance of the GaN layer and further influence the internal quantum efficiency of the LED accordingly.
The lateral epitaxial growth of the GaN epitaxial layer on the substrate is commonly achieved by a process of lateral epitaxial overgrowth or suspension epitaxial growth so as to reduce the density of defects in the epitaxial layer and improve the quality of crystal in the epitaxial layer. However, the process includes two steps during which the growth of the epitaxial layer may be disturbed. Moreover, the process is not only complicated but also costs too much. Therefore, the fabricating and the application of such LEDs are limited. The lateral epitaxial growth of the GaN layer may also be achieved by a substrate having patterned areas. But the lateral epitaxial growth of the GaN layer may only be performed in the patterned areas, while the lateral epitaxial growth may not be performed in the remaining areas. In such remaining areas, the defect density is still very high, for example, 108, and consequently existence of nonradiative recombination centers may be caused. Accordingly, the internal quantum efficiency and the performance of the LED may be reduced.